CONTINUOUSLY MONITORING oil, gas and chemical pipe lines and tanks for small and large leaks has been a problem for a long time. In some areas, authorities require strict surveillance for small leaks, less than one gallon per day, as well as rapid detection and reporting of large leaks to protect the environment.
None of the usual methods, including comparison of flow or pressure differences, periodic pressure testing, and pig techniques have offered satisfactory detection sensitivity or leak location. This invention was conceived and developed to meet this need.
Other systems for testing for leaks have relied on indirect, inferential detection. That is, a condition caused by the leak, such as pressure loss or volume imbalance, was first detected and used as an indication of a leak. Later systems developed for direct sampling for presence of vapors or gases from leaks have used continuous aspiration of air samples for detection of large leaks, but involve too much dilution of the sample to be able to detect medium to small leaks. Later systems developed for testing of columns of dormant air samples for presence of diffused vapors or gaseous indications of leaks have been effective for detecting and locating small leaks, but depend on cycle testing involving prolonged periods of dormancy for adequate time for diffusion, and thus do not provide the quick, early emergency response required for large leaks.
The present invention is a dual, periodic air-sampling system for small leaks, combined with constant displacement or aspiration of continual flow of a column of air, developed because conventional leak-detection systems did not offer satisfactory sensitivity and rapid response for leak location.
This invention is able to provide direct leak detection instead of inferential, and it provides both cycle, periodic testing for diffusion from small leaks, combined with continuing, rapid sampling for large leak. That is, the leaking liquid or gas itself is detected, not a condition caused by the leak, such as pressure loss or volume imbalance. This system is not affected by operational transients and ambient conditions existing in the soil.
Before development of this invention, the original diffusion detection system was built to detect extremely small leaks of 0.4 1./day on a liquid pipeline, over a long period of time. To do this it evacuated, displaced or pulled the air out of the sensor tubing just once every day. This allowed the leaking fluid's vapor to form quite a large concentration slug in the sensor tube, large enough for the detector to sense an extremely small leak. This original system provided for leak detection alarming once every 24 hours, but most environmental authorities today require a continuous monitoring and alarming leak-detection system which would alarm on any dangerous leak within 30 minutes, not 24 hours. For early response, such a system requires the set up of a detector-pump unit to evacuate the sensor tube continuously. Such continuous evacuation sensing is needed to provide the emergency response mode. But the emergency response mode would not detect small leaks which require long periods of diffusion for detection.
For an improved system to meet the latest environmental requirements for combined reliable detection for small leaks concurrently with emergency response for large leaks, the following was required:
Continuous leak-detection monitoring and alarming. PA1 Response to any leak within 30 minutes. PA1 All installations less than 18 inches above grade. PA1 Length of monitored right-of-way more than 10 miles. PA1 Accessibility. PA1 Not an obstacle or an eyesore.
Such a system would need to operate in two different modes: The low-level leak detection mode similar to the original patented leak alarm system for pollutants, and the emergency-response mode for high-level rapid detection of large leaks.